The Efficacy of Accelerating Orthodontic Tooth Movement by Combining Self-Ligating Brackets With One or More Acceleration Methods: A Systematic Review

This review aimed to evaluate the effectiveness of using one or more acceleration methods with self-ligating brackets to accelerate orthodontic tooth movement in adults and the associated effects of these interventions. An electronic search of the following databases (PubMed, Scopus, Google Scholar, EMBASE) was performed (From January 1990 to November 2021). ClinicalTrials.gov and the International Clinical Trials Registry Platform were also electronically searched to find any unpublished studies and ongoing trials. The selected randomized controlled trials (RCTs) involved adult patients treated using self-ligating brackets combined with one or more acceleration methods compared with self-ligating brackets or conditional brackets alone. The risk of bias was assessed using Cochrane’s risk of bias tool. A total of seven RCTs and one controlled clinical trial (CCT) were included in this review. Combining self-ligating brackets with flapless corticotomy, low-level laser therapy (LLLT), and infrared light accelerated orthodontic movement by 43% and 50% for surgical methods, 20-50% for LLLT, and 22% for infrared light. Regarding side effects on periodontal tissues, neither flapless corticotomy nor low-frequency vibrational forces caused any damage. Combining self-ligating brackets and flapless corticotomy, low-level laser, or infrared light effectively accelerated orthodontic movement by 20% to 50 %. In contrast, the combination of self-ligating brackets with vibrational forces did not affect speeding tooth movement. The acceleration methods did not have any side effects on the periodontal tissues, but the available evidence was insufficient. There is a need for further primary research regarding the effectiveness of combining self-ligating brackets with acceleration methods and the possible untoward side effects.


Introduction And Background
The use of self-ligating brackets in orthodontic treatment has become popular recently, which allows orthodontists to abandon the traditional means of archwires ligation (i.e., stainless steel ligatures and elastomeric modules) [1]. Depending on the locking mechanism, self-ligating brackets are classified into two main types: active self-ligating brackets (ASLBs), which lock tightly on the wire to express better rotation and torque values, and passive self-ligating brackets (PSLBs), which allow sliding movements [2]. An additional type of self-ligating brackets results from the combination of both active and passive brackets [3]. This type may result in greater efficiency in the expression of tip and torque values, faster movement of the anterior teeth, and lower loss of the anchorage [3]. There are many claims about the advantages of selfligating brackets (SLBs) compared with conventional brackets (CBs) in dramatically reducing chair-side time, reducing the total treatment time, gaining better oral health, and causing less pain and discomfort [4].

Study selection and data extraction
The eligibility of the trials was estimated by two reviewers (HMA and MYH) separately, and if there were any odds, a third author (EZ) was asked to settle this. First, the titles and abstracts only were checked. Full-text estimation as a second step for all relevant papers and elected for implication. Full-text estimation was also done when the titles or abstracts were not obvious. The documents which did not conform to one or more of the inclusion criteria were kept out. For any elucidation or extra details, the corresponding authors were emailed.
The two authors (HMA and MYH) extracted data independently in the predefined tables for extracted data. To resolve any disagreements between the two authors, a third author (EZ) was consulted. The following elements were listed on the data extraction sheet: basic information (authors' names, publication year, and study location); methodology (research design: either a split-mouth design (SMD) or a parallel-group design (PGD), comparison of several treatments); participants (age, gender, sample size); intervention (location, type, technical characteristics); orthodontic consideration (malocclusion types, features, and biomechanics of applied devices, follow-up duration); and outcomes (primary and secondary outcomes mentioned, measurement methods, statistical significance of differences between experimental and control groups).

Assessment of risk of bias in included studies and strength of evidence
Using Cochrane's risk of bias tool, the two reviewers (HMA and MYH) evaluated the quality of the included studies [32]. If there were any disagreements, a third author (ASB) was asked to make a final decision. The risk of bias for the following fields was rated as low, high, or unclear: sequence generation (selection bias), allocation concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessors (detection bias), incomplete outcome data addressed (attrition bias), selective outcome reporting (reporting bias), and other bias.
The following criteria were used to determine how likely each trial was to be biased overall: if all fields were considered to have a low risk of bias, the trial would be viewed at a low risk of bias where bias is unlikely to alter the outcomes significantly; if one domain at least or more were determined to have an uncertain risk of bias, the trial would be deemed to have an unclear risk of bias, which releases some doubt on the outcomes; and if one domain at least or more were decided to have a high risk of bias, the trial would be assessed at high risk of bias where bias impact the outcomes critically.

Study Selection and Inclusion in the Review
In the electronic search, 1367 references were discovered and eight more records were identified from other sources. Repeated references were omitted then 559 citations were carefully checked. A comprehensive screening of the titles and abstracts was accomplished for eligibility, and the papers not fulfilling the inclusion criteria were discarded. As a result, 12 trials were likely related and were thoroughly reviewed. Following the full-text reading of the publications, four studies were eliminated ( Table 2). Ultimately, seven RCTs and one CCT were included. The PRISMA flow diagram is shown in Figure 1.
This study aimed to examine the effects of low-energy laser irradiation on stimulating keratinized gingiva in patients with teeth that erupted in oral mucosa completely, not the effect of the participation of self-ligating brackets with acceleration methods on orthodontic movement. This study aimed to compare the effect of using self-ligating brackets or conventional brackets with micro-osteoperforation (MOP) on the space closure rate without the existence of the control group (self-ligating brackets alone/conventional brackets alone).

Risk of Bias of Included Studies
The summary and the overall risk of bias for the enclosed RCTs are depicted in Figures 2, 3. Table 4 shows the risk of bias for the non-randomized study according to the MINORS (Methodological Index for Non-Randomized Studies) tool. Two RCTs were classified as 'low risk of bias' [25,38]. Two RCTs were judged to be at an 'unclear risk of bias' [34,37] while the three others were assessed as having a 'high risk of bias' [33,35,36]. The random sequence generation and the participants' blinding were evaluated as a 'high risk of bias' in three RCTs, and the blinding of outcomes assessors was assessed as a 'high risk of bias' in two RCTs. The allocation concealment was unclear in three RCTs. More information about the risk of bias can be seen in Table 5. For the only CCT included [40], according to the MINORS tool, the most problematic domains were the inclusion of consecutive patients and prospective calculation of the study sample size. The risk of bias score was 19/24, which meant fair quality.    Out of the eight studies, two studies only assessed the influence of combining surgical methods (using flapless corticotomy in particular) with SLBs [25,33], and the other six studies evaluated combining physical methods with SLBs [34][35][36][37][38]40]. Three of those six studies included LLLT with SLBs [36,38,40], one involved infrared light [35], and the other two studies assessed low-frequency vibrations with SLBs [34,37].
Combining flapless corticotomy with SLBs: Two parallel-group design studies evaluated the effectiveness of combined SLBs with piezocision [25,33]. Charavet et al. conducted their study on 24 adult patients with mild to moderate crowding, where they found a 43% decrease in total treatment time when using SLBs with piezocision compared to the traditional orthodontic treatment [33]. As for the study of Al-Ibrahim et al. on 58 patients with severe crowding on the upper jaw, it was shown that the participation of self-ligating brackets with the flapless corticotomy contributed to an acceleration of orthodontic movement by 50% [25].
Combining low-level laser therapy (LLLT) with SLBs: There are one split-mouth design study [36] and two parallel-group design studies evaluated using the low-level laser with self-ligating brackets [38,40].
Qamruddin and his colleagues experimented on 20 patients with a Class II division 1 malocclusion using the split-mouth design [36]. They found that the retraction of the canines on the experimental side was greater compared to the control group (1.6 mm/month vs. 0.79 mm/month, respectively) [36].
For the two parallel-group design studies, Lalnunpuii et al.'s study focused on the investigation of en-mass retraction in young patients and concluded that the rate of orthodontic movement was faster in the experimental group compared to the control group (≃ 0.66 mm/month vs. 0.48 mm/month; respectively) [38]. The other study focused on assessing decrowding in adult patients, where it found that the combination of SLBs with the LLLT accelerated the correction of lower crowding by 20% [40].
Combining low-frequency vibrations with SLBs: For this field, two studies of three-arm design were found [34,37]. One study experimented on a group of adult patients who had crowding on the lower incisors without the need for extraction [34], and the other study was on young patients who underwent en-mass retraction [37]. Both studies did not find any effect of the low-frequency vibrational forces on accelerating the rate of orthodontic tooth movement.
Combining infrared light with SLBs: There is only one trial with a parallel-group design conducted by Nahas and his colleagues [35]. They investigated using self-ligating brackets with extraoral infrared light for 20 minutes/day compared to a control group [35]. They conducted their study on 20 patients with moderate dental crowding cases and concluded that the participation of self-ligating brackets with infrared light contributed to the acceleration of leveling and alignment by 22% [35].

The Secondary Outcomes: The Periodontal Status
Three studies examined the periodontal status associated with the participation of one of the acceleration methods with self-ligating brackets [25,33,34]. In Charavet's study on 24 adult patients who needed decrowding on both jaws without extraction, they found no gingival recession following piezocision with SLBs [33]. Kalemaj et al. found no negative effects on periodontal depth after applying low-frequency vibrational forces with SLBs [34]. Furthermore, Al-Ibrahim et al. found that applying flapless corticotomy with self-ligating brackets had no adverse effects on periodontal indices [25].

Discussion
This systematic review is the first in the literature to evaluate the efficiency of the combination of selfligating brackets with different acceleration methods in various malocclusion cases. The current systematic review performed a qualitative evaluation including 339 patients in eight selected clinical studies.
To reduce confounding factors, the selection of studies was confined to randomized and non-randomized controlled clinical trials only. A quarter of the included studies were rated at low risk of bias. On the other hand, the blinding of patients and the random sequence generation were considered the most problematic fields in the other studies.
The two studies that evaluated the combination of self-ligating brackets with surgical methods using flapless corticotomy showed an acceleration of 43% and 50% [25,33]. The acceleration obtained in these two studies can be explained by the effect of participating in the regional acceleratory phenomenon (RAP) with the mechanical effect of self-ligating brackets [25,33] [25].
Regarding the six studies that evaluated the effect of participation of self-ligating brackets with physical methods, low-level laser and low-level light combined with self-ligating brackets were effective in accelerating the orthodontic movement [35,36,38,40]. In contrast, the vibrational forces had no positive effect [34,37].
The rate of acceleration with low-level laser ranged between 20% and 50% (50%, 37.5%, and 20% in Qamruddin, Lalnunpuii, and Chandran studies, respectively) [36,38,40]. The variances can explicate these differences in the length and energy of the laser beam and the application protocols.
The 22% acceleration rate when using infrared light can be explained by the biological effects of low-level light [35]. Red and infrared lights are considered the most effective irradiation because hemoglobin does not absorb light in this range, and therefore the light can infiltrate deep into the living tissues and induce photobiomodulation [34,37]. The cytochrome oxidase and the mitochondrial enzyme, which are involved in the production of ATP, are upregulated by infrared light [34,37]. Any localized rise in ATP levels causes cells to undergo a remodeling process due to increased metabolic activity and promote their division and proliferation, which will help speed up tooth movement [34,37].
The lack of acceleration in the two studies applying low-intensity vibrational forces could be explained by the fact that the mechanical stimulation released by these forces is weak and unable to activate bone remodeling. The only effect of these forces was only IL-1β levels increasing, which had no impact on the rate of orthodontic movement.
All three studies that evaluated the status of periodontal tissues did not find any side effects following the studied therapeutic interventions (flapless corticotomy and vibration forces) [25,33,34]. This could be elucidated by the nature of evaluated surgical or physical interventions, which were not invasive.

Limitations of the current review
About three-quarters of the included studies were not at low risk of bias (two studies had some aspects of bias, and three were at high risk of bias). Thus, more low-risk of bias randomized controlled clinical trials are required to evaluate the effectiveness of combining self-ligated brackets with different acceleration methods. Five of eight studies did not evaluate the side effects of applying acceleration methods. Moreover, the side effects studied in the remaining three studies were not comprehensive, and therefore it was difficult to give a clear assessment regarding side effects due to the lack of available information. Most studies did not assess the entire duration of the studied orthodontic treatment. Long-term follow-up of the studied interventions was also absent in all included trials.

Conclusions
The combination between self-ligating brackets and flapless corticotomy, low-level laser, or infrared light effectively accelerated the orthodontic movement by 20% to 50%. In contrast, the combination of selfligating brackets with vibrational forces had no effect on speeding tooth movement. The acceleration methods used did not have any side effects on the periodontal tissues, but the available evidence was insufficient. There is a need for further primary research regarding the effectiveness of combining selfligating brackets with acceleration methods, as well as the consequent side effects.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.